The V8 Owners Forum -

Where / how are you measuring the boost and can you post pictures of all your plumbing between the s/c and the carbs.

Hi Elliot
If you look at the pic on the first post the cabs are 1.75 SU bolted to the back of the supercharger in a suck through format there is not realy any plumbing as such. the pressure is taken off the a tapping in the manifold above the intake of cylinder number 8. The camshaft is a Crower 50299. If more pics help I will post more tonight.
Mick

stevieturbo wrote:It is highly unlikely the carbs are posing that much of a restriction.

well maybe the carbs alone. but with a particularly windy intake (looks like there could be some tight bends between the carb and charger entry) and two small su carbs they could sum up to a large restriction

remember superchargers are very good at pushing air but not that great at sucking it.

with a 20mm restrictor (regulation) our old 600cc formula car produced no boost anywhere in the rpm range as the charger (lysholm/autorotor 1050) had to go after the restrictor. it did beef the torque curve up quite a bit below 8000 rpm, but after that (up to 12,000) there was a very strong vacuum that used to try and crush all the samco hoses. they had to be reinforced with ally stiffners.

ok the example is a little extreme as 20mm is a pretty small restrictor even with a properly designed venturi profile, but it could possibly drop the boost from .1 above atm to .2 below...

Texpis, I for one would be interested to see some more photos. I can't really make out the plumbing joining the two Sus to the Supercharger. Can't visualise it in my imagination either. What RV8 donor vehicle did you source the blower from? Did you take any snapshots of the blower and intake before you fitted it?

Hi All and thanks for the interest. The carbs are twin SU mounted on a box bolted directly on to the back of the blower, it gives the illusion of the SU mounted on the manifold like the original V8 SU manifold. The manifold and Blower came of a sudi imported landrover 110 3.5. I didn't see the setup on the original vehicle. The paperwork I got with it (Some typed instructions on how to fit ) has SUPERCHARGER SYSTEMS LTD Saudi Spec Landrover VS Supercharger. My engine is a 4.2 with crower 229 cam and janspeed through exhaust. the charger defiantly makes a difference in torque up to about 3000 which most off the time off road on an autobox is great. But the boost seems to stop at 0.1 bar. I have included some pics it is difficult to see even from the pics.

From the picture it looks like the guage pickup is going to measure vacumn and not boost

I take it that vacuum pipe is for the dissy? Not exactly a free flowing setup where the carbs bolt on the the back of the SC- the air flow through the carbs and round the corners must be terrible, if it was me I would start by taking the 'box' off the rear the SC and modifying it or making a new one so the carbs are pointing at the rear of the SC or so they sit further out and have a nice sweeping bend into the back of the SC, wouldn't be hard to do and even if it is not the cause of the lack of boost- it would certainly help a great deal!

TC

Hi the pipe is for megasquirt it used to be efi now it controls the spark the coil pack you can see in pic 1. The pressure is taken of the inlet manifold just above number 8 cylinder. Will bigger carbs help in the short term? It’s the playing season now won’t have time to change anything radical until autumn.

Mick

I think you would get the biggest benifit per £ spent getting a feed of cold air to the carbs you have, especially if that is in a 4X4 that spends most of its time crawling along under 20mph. Get a heat deflector above the exhausts, arrange to blow some cold air into the bottom of the engine bay, make somewhere for the hot air to go that takes it away from the top of the engine bay and route a cold air directly into the carbs from outside the engine bay, I recon you wouls see a big jump in power if you got that side sorted.
Mike

Now I can make out what's what. I admit to having not quite believed the first photo you posted, looked a lot like a blower plonked in front of a twin SU manifold like my P6 left the factory with, but I didn't really think anybody would bother faking a blower installation! All is now clear. Doesn't really help you get it working better but certainly satisfied my curiosity, and has set my brain fizzing with a similar idea...

Yea the system seems to have been set up to look simulare to a standard SU set up with a blower in front why I dont know. It is on a 4X4 a bowler tomcat. I could do with a raised air intake so that will put cold air into the carb will have to be carefull not to choke it. Is the concensus that the blower is big enough? If no I will look into plan B!

Mick

texpis wrote:Hi the pipe is for megasquirt it used to be efi now it controls the spark the coil pack you can see in pic 1. The pressure is taken of the inlet manifold just above number 8 cylinder. Will bigger carbs help in the short term? It’s the playing season now won’t have time to change anything radical until autumn.

Mick

So doesnt the ignition have any ability to compensate for boost ? Where you have the take of..it will only measure vacuum.

If the blower came off a 3.5 and is now on a bigger capacity engine I would think that it is " starving" the engine due to being set-up for a smaller volumetric flow, hence the vacuum reading.
The only fix could be going higher on the overdrive pulley to deliver more air but that will drop your redline revs.

If it can't be used, chuck it in the post and I will look after it for you.......

another thought... twin su's dont even flow enough for a performance 3.5, let alone a supercharged 4.2

there is a good chance there is sonic flow (and hence choking) through the venturis in the carbs.

a 4 barrel would be the best bet (there wouldnt be space for quad webers etc) however it would make the assembly taller and would obviously mean a new manifold would be needed

yes megasquirt can compensate for boost but I am still learning and I thought running it the standard way will get me away while I sort the teething problems. do you need a dififerent MAP sensor in the megasquirt to run boost. I thought the carbs could be too small for the engine.

Mick